So is there no way to connect the TV tuner to the car's antenna to improve the reception to match the quality to that of a head unit?

OK, you really need to start doing some searching in the forums at this point.
There have been a great many solutions and projects attempted. Some of those are still underway and are likely to come to fruition in the near future.

You're not asking new questions and there are no new answers, so why not give the same old answers to teh same old questions an opportunity to be of use to someone.

Yeah there do seem to be a few options around the forum. Unfortunately it is a little difficult with the FM solutions. Can't wait 'till everything's satellite but then i know nothing about it it's probably even more complex
In any case I for one will be keeping some sort of head unit. Maybe a hidden one would be worth it? Like the othhers have said it depends on your preference and how much radio you listen to.

There is a post somewhere on here about a device that has an external antena, i think the guy had to hang it out his window

I am keeping a head unit only because I like to turn a knob to adjust the volume. I know I could use a Griffin powermate to do it, but I need AM radio as well. So I have two reasons, plus, the FM card I tried had horrible reception. If you want TV reception, you'll need a different antenna. The FM antenna on cars today won't do much for tv reception. Now if you want satellite (although too much for just a car IMHO), that's a different story.